Method and corresponding apparatus for producing iron from direct reduction of iron ore

ABSTRACT

A method for producing direct reduced iron is provided. The method includes circulating a first stream of spent reducing gas exiting a reactor in a reducing gas circuit through at least one carbon dioxide removal unit and a reducing gas heater and the reactor. The method also includes mixing the first stream with reducing gas containing heavier hydrocarbons than methane.

FIELD OF THE INVENTION

The present invention concerns a method and corresponding apparatus forproducing metallic iron by means of direct reduction of iron ore, usinga reducing gas produced from a hydrocarbon source having carboncompounds heavier than methane with limited formation of carbonresidues.

BACKGROUND OF THE INVENTION

It is known that, in the steel industry, one of the most widely usedprocesses for producing metallic iron is the direct reduction of ironore (Direct Reduced Iron, DRI). This DR (Direct Reduction) process isadvantageous in particular due to its low environmental impact and highefficiency.

The DR process provides to make the iron ore react with a stream ofreducing gas in a suitable reduction reactor.

The reducing gas mainly comprises hydrogen (H₂) and carbon monoxide (CO)by means of which the oxygen is in fact removed from the iron ore bymeans of a high temperature chemical reduction (700° C.-1000° C.) asindicated by the following formulae:

Fe₂O₃+3H₂→2Fe+3H₂O (1) ΔH25° C.=−95.484 kJ/kmol

Fe₂O₃+3CO→2Fe+3CO₂ (2) ΔH25° C.=−28.085 kJ/kmol

Usually, the reducing gas used in these processes is produced from amixture of a fresh reducing gas, that is CH₄ and heavy hydrocarbons highcontent gas introduced from outside and spent reducing gas that exitsthe reactor after the reduction process.

The spent reducing gas can be reused in new reducing operations, aftertreating said gas in order to restore its reducing characteristics andpossibly mix it with fresh reducing gas, for example, natural gas orCoke Oven Gas (COG) or other synthetic gases with high content of CH₄and heavy hydrocarbons.

Natural gas, the main source of reducing gas in DRI processes,comprises, in varying proportions, hydrocarbons such as methane (CH₄)and ethane (C₂H₆) and possibly other longer chain hydrocarbons (C2+),that is heavier, such as propane (C₃H₈), butane (C₄H₁₀) etc. in variableproportions.

COG which is produced by pyrolysis of coal, has a high proportion ofcarbon compounds such as Benzene, Toluene and Xylene, known as BTX, andother complex carbon compounds and can also be used as source ofreducing gas.

Before being put into contact with the iron ore inside the reactor, thereducing gas coming from any gas source with high content of CH₄ andheavy hydrocarbons (mixed with the recirculated spent reducing gas) isgenerally heated to increase its temperature to a value comprisedbetween 700° C. and 1100° C. in a gas heater. The reducing gas must beheated to such a high temperature to provide heat to the iron oxidesmaterial inside the shaft furnace so as to maintain adequate temperatureconditions for the kinetics of the reduction reactions to be within therequired value corresponding to the DRI production rate of the furnace.

It is known that, when the C2+ hydrocarbon content is not negligible,during the heating the undesired breaking of the chains of thehydrocarbons, and the consequent deposit of solid carbon inside theheater, occur.

One disadvantage, therefore, is the need to periodically perform longcleaning operations of the heater to remove the carbon deposits.

Another disadvantage is the interruption of production during thecleaning operations of the heater to remove the carbon deposits, causingan economic loss.

Another disadvantage is that frequent thermal cycles of the heater,determined by the need to carry out the cleaning cycles, can lead to apremature deterioration thereof.

It is also known to use devices to remove, at least partially, thefraction of heavier hydrocarbons from the reducing gas, such as, forexample, the so-called “reformers”.

One disadvantage of these devices is that they increase the capitalexpenditure (CAPEX) of the apparatus.

Another disadvantage is that devices such as the external reformers makethe reducing apparatus more complex.

US 2001/0003930 A1 discloses method and apparatus for increasing theproductivity of a direct reduction process in which iron oxide isreduced to metallized iron by contact with hot reducing gas; comprisingthe steps of: a) providing a first hot reducing gas consistingessentially of CO and H₂; b) providing additional reducing gas byreaction of a gaseous or liquid hydrocarbon fuel with oxygen; c) mixingthe first hot reducing gas with the additional reducing gas to form areducing gas mixture; d) enriching the reducing gas mixture by theaddition of a gaseous or liquid hydrocarbon; e) injecting oxygen oroxygen-enriched air into the enriched mixture; and f) introducing theenriched mixture into an associated direct reduction furnace as reducinggas. However, this document is completely silent regarding the depositof solid carbon inside the heater due to the fraction of heavierhydrocarbons present in the natural gas.

WO 2016/203396 A1 discloses natural gas mixtures enriched with heavierhydrocarbons to improve the heating values to obtain a reducing gasstream that is then subjected to a reformer. This document as well doesnot face the problems regarding the deposit of solid carbon inside theheater due to the fraction of heavier hydrocarbons present in thenatural gas.

DE 40 30 093 A1 discloses a process for the direct reduction of granulariron ore in a furnace with a hydrogen and carbon monoxide-containingreducing gas, which is produced from a methane-rich gas over anindirectly heated catalyst at temperatures of 800 to 1200° C., whereintop gas is withdrawn from the furnace and at least partly used as fuelfor indirect heating of the catalyst. This document discloses that anatural gas is supplied to the heat exchange zone, the ethane content ofwhich is at least 25% by volume and which contains 0.5 to 5% by volumeof propane and 0.1 to 5% by volume of butane and higher hydrocarbons. Ifsuch natural gas together with water vapor and/or CO₂ is passed throughthe catalyst, which is indirectly heated in the tube furnace, aftersufficient heating, soot deposits lead to the rapid deactivation of thecatalyst. This document aims at suppressing as far as possible thedisturbing soot formation in order to achieve a long service life of thecatalyst, however this is achieved via a specific treatment to removeheavier hydrocarbons present in the natural gas.

WO 2018/024767 discloses a method and apparatus for producing directreduced iron utilizing a catalytical pre-treatment of hydrocarbons as asource of reducing gas. This document teaches how to obviate to thepresence of heavier hydrocarbons present in the natural gas by treatingthe natural gas in a pre-reforming section, before being supplied.

There is therefore a need to perfect a method and an apparatus forproducing DRI from direct reduction of iron ore that can overcome atleast one of the disadvantages of the state of the art.

In particular, one purpose of the present invention is to provide amethod and corresponding apparatus for direct reduction of iron oreutilizing reducing gas having a high content of hydrocarbons heavierthan methane (>4%) which is able to produce DRI limiting the formationof carbon deposits in the heater.

Another purpose of the present invention is to provide a method and anapparatus for direct reduction of iron ore that is efficient andcontains investment costs.

The Applicant has devised, tested and embodied the present invention toovercome the shortcomings of the state of the art and to obtain theseand other purposes and advantages, solving the technical problem oflimiting the amount of hydrocarbons heavier than methane or complexcarbon compounds passing through the reducing gas heater of a DRapparatus and thus decreasing the amount of carbon deposits that mayform therein, while at the same time maintaining the temperature of thereducing gas and iron oxides in the shaft furnace to give the desiredproduction rate of DRI.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independentclaims, while the dependent claims describe other characteristics of theinvention or variants to the main inventive idea.

Embodiments described here concern a method for producing DRI in adirect reduction process using reducing gas chosen among a natural gashaving a high content of total hydrocarbons heavier than methane (>4%),or coke oven gas (COG) having complex carbon compounds (BTX) or othersynthetic gases coming from any source with high content of CH₄ andheavy hydrocarbons.

According to one embodiment, the method comprises circulating a firststream of reducing gas exiting a reactor in a reducing gas circuitthrough at least one carbon dioxide removal unit, a reducing gas heaterand a reactor.

The method further provides to feed into the reducing gas circuitbetween the reducing gas heater and the reduction reactor, a stream offresh reducing gas which amounts to more than 20% of the overallquantity of reducing gas sent to the reduction reactor and thus neededto operate the direct reduction process.

The remaining part not fed in this position is instead injectedaccording to the classic method between the carbon dioxide removal unitand the reducing gas heater.

The present description also concerns an apparatus for producing ironfrom direct reduction of iron ore using a reducing gas having a highcontent of total hydrocarbons heavier than methane (>4%), chosen among anatural gas having a high content of hydrocarbons heavier than methane,or coke oven gas (COG) having complex carbon compounds (BTX) or othersynthetic gases coming from any source with high content of CH₄ andheavy hydrocarbons. According to one embodiment, the apparatus comprisesa reduction reactor, a carbon dioxide removal unit and a heater, areducing gas circuit being provided which passes through the carbondioxide removal unit and the heater and the reactor.

According to one embodiment, the apparatus comprises first injectionmeans configured to feed, into the reducing gas circuit between thereducing gas heater and the reduction reactor, a stream of freshreducing gas which amounts to more than 20% of the quantity of reducinggas needed to operate the direct reduction process, while maintainingthe total amount of energy necessary to carry out the reductionreactions in the reactor according to the programmed production rate. Asthis energy for the reduction reactions is provided by the sensible heatof the reducing gas stream fed to the reactor, and this heat is suppliedto the reducing gas in the heater, it may be necessary to preheat saidstream of reducing gas in a separate heater up to a temperature below650° C. to avoid carbon deposits in this separate heater.

In some embodiments, the method and apparatus described hereadvantageously provide to recover and regenerate the reducing gas, wasteof the reduction reaction, without the addition of further apparatusessuch as, for example, an external reformer.

Advantageously, the method does not comprise any step of removal of thefraction of heavier hydrocarbons from the reducing gas, in particular itdoes not comprise any reforming step. Further, the apparatus describedherein does not comprise any means or device for removal of the fractionof heavier hydrocarbons from the reducing gas, in particular it does notinclude any reformer.

According to some embodiments, the spent reducing gas exiting thereactor can enter the reducing gas circuit after suitable regenerationand be re-introduced into the reactor.

With the term “regenerate” we mean the set of processes, performed byregeneration devices, suitable to at least partly restore the reducingproperties of a reducing gas.

Furthermore, some embodiments provide that the spent reducing gas can bemixed with reducing gas before being injected into the reactor and/ormixed directly inside the reactor.

In accordance with possible embodiments, the reducing gas circuit of thereduction apparatus described here comprises at least one carbon dioxideremoval unit suitable to remove the CO₂ from the reducing gas.

In accordance with possible embodiments, the method also provides toinject a greater volume, with respect to the state of the art, ofreducing gas inside the circuit to be mixed with the spent reducing gas,in order to promote the reforming reactions directly inside thereduction reactor.

Preferably, this greater volume of reducing gas is injected in a pointof the reducing gas circuit downstream of the heater.

Advantageously, in this way the long chain hydrocarbons (C2+) possiblypresent in the fresh reducing gas, such as natural gas, COG, or othersynthetic gases coming from any source with high content of CH₄ andheavy hydrocarbons, do not come into contact with the elements of theheater, avoiding the deposit of carbon inside it.

In this way, even the use of reducing gas possibly with a highpercentage of long chain hydrocarbons (C2+), that is the use of naturalgas or the use of COG containing BTX or the use of other synthetic gasescoming from any source with high content of CH₄ and heavy hydrocarbonsis made possible without the risk of formation of carbon deposits in theheater.

According to the method and apparatus of the present disclosure, thepresence of heavier hydrocarbons present in the natural gas leading todeposit of solid carbon inside the heater is solved without any specifictreatment or pre-treatment of the natural gas, as in the case of theknown prior art, but on the contrary advantageously supplying thenatural gas in a specific zone where the presence of heavierhydrocarbons in the natural gas is not dangerous, in particular feedingthe stream of fresh reducing gas, which amounts to more than 20% of thequantity of reducing gas needed to operate the direct reduction process,into the reducing gas circuit between the reducing gas heater and thereduction reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will becomeapparent from the following description of some embodiments, given as anon-restrictive example with reference to the attached drawings wherein:

FIG. 1 is a schematic representation of an apparatus for implementing amethod according to the embodiments described here.

To facilitate comprehension, the same reference numbers have been used,where possible, to identify identical common elements in the drawings.It is understood that elements and characteristics of one embodiment canconveniently be incorporated into other embodiments without furtherclarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

We will now refer in detail to the various embodiments of the presentinvention, of which one or more examples are shown in the attacheddrawings. Each example is supplied by way of illustration of theinvention and shall not be understood as a limitation thereof. Forexample, the characteristics shown or described insomuch as they arepart of one embodiment can be adopted on, or in association with, otherembodiments to produce another embodiment. It is understood that thepresent invention shall include all such modifications and variants.

Before describing these embodiments, we must also clarify that thepresent description is not limited in its application to details of theconstruction and disposition of the components as described in thefollowing description using the attached drawings. The presentdescription can provide other embodiments and can be obtained orexecuted in various other ways. We must also clarify that thephraseology and terminology used here is for the purposes of descriptiononly, and cannot be considered as limitative.

Embodiments described here concern a method for producing DRI in adirect reduction process using a reducing gas chosen among a natural gashaving a high content of total hydrocarbons heavier than methane (>4%),or coke oven gas (COG) having complex carbon compounds (BTX) or othersynthetic gases coming from any source with high content of CH₄ andheavy hydrocarbons. It is understood that by hydrocarbons heavier thanmethane we mean the sum off all hydrocarbons with two or more carbonatoms (C2+). Possible examples are ethane (C₂H₆), propane (C₃H₈), butane(C₄H₁₀) or higher. Thus, the expression “high content of totalhydrocarbons heavier than methane” as used in the embodiments describedherein means that the sum off all hydrocarbons with two or more carbonatoms (C2+) is more than 4%.

The method can be favourably implemented by means of an apparatus 100for example as shown in FIG. 1 .

The method according to the present description comprises circulating afirst stream F1 of reducing gas exiting from a reduction reactor 10 in areducing gas circuit 20 through at least one carbon dioxide removal unit38 and a reducing gas heater 42 and a reactor 10.

According to one aspect of the invention, the method provides to feed,into the reducing gas circuit 20 between the reducing gas heater 42 andthe reduction reactor 10, a stream F2 of fresh reducing gas whichamounts to more than 20% of the overall quantity of reducing gas sent tothe reactor 10 and thus needed to operate the direct reduction process.

In possible implementations, the stream F2 of said reducing gas amountsto more than 25%, or 30%, or 35%, or 40%, or 45%, or 50%, or 55%, or60%, or 65%, or 70%, or 75%, or 80%, or 85%, or 90%, or 95%, of thequantity of the reducing gas needed to operate the direct reductionprocess.

In accordance with some embodiments, the method can provide that thestream F2 of gas is pre-heated to a temperature below 650° C.

According to some embodiments, the pre-heating of the stream F2 canoccur in a convective zone 43 of the reducing gas heater 42.

In other embodiments, the stream F2 can be pre-heated in a heatexchanger or fired heater separate from the reducing gas heater 42.

In further embodiments, the stream F2 can be injected into the reducinggas circuit 20 without being pre-heated.

According to some embodiments, the method can provide to feed at leastone other streams F3, F4 of fresh reducing gas, which amounts to theportion of reducing gas not injected into the reducing gas circuit 20 bythe stream F2.

In a possible embodiment, the stream F3 can be injected incorrespondence with any portion whatsoever of the reducing gas circuit20 located between the carbon dioxide removal unit 38 and the reducinggas heater 42.

In another possible embodiment, the stream F4 can be injected directlyinto the reactor 10.

In another possible embodiment, it is conceivable to perform a combinedfeed of reducing gas which amounts to the portion of reducing gas notinjected into the reducing gas circuit 20 by the stream F2, formed bythe stream F3 injected in correspondence with any portion whatsoever ofthe reducing gas circuit 20, located between the carbon dioxide removalunit 38 and the reducing gas heater 42, and by the stream F4 injecteddirectly into the reactor 10.

Some embodiments can also provide that at least the second stream F2,and possibly one and/or the other of the streams F3, F4, are controlledby at least one control unit 68 of the apparatus 100, configured toregulate the flow rate and therefore the percentage of reducing gasinjected into the reducing gas circuit 20.

According to embodiments, the control unit 68 may regulate the flow rateof the gas stream F2 in response to a signal emitted by a flow ratesensor 69 and/or 70 measuring the flow rate of gas stream F3 and/or F4.

In other embodiments, control unit 68 additionally to regulating theflow rate of gas stream F2 also may regulate the flow rate of gas streamF3 and/or F4.

In other embodiments, not shown here, each stream F2, F3, F4 can becontrolled by a respective and dedicated control unit, which can beconnected to each other.

In some embodiments the control unit 68 may also regulate a flow rate ofoxygen 52 with the aim of compensating the loss of energy caused by thefact that gas stream F2 bypassing the fired heater 42 will not have inany case the same temperature of the pipe 28 after heating in same firedheater 42.

FIG. 1 is used to describe embodiments of an apparatus 100 for producingiron from direct reduction of iron ore using reducing gas having a highcontent of total hydrocarbons heavier than methane (>4%), chosen among anatural gas having a high content of hydrocarbons heavier than methane,or coke oven gas (COG) having complex carbon compounds (BTX) or othersynthetic gases coming from any source with high content of CH₄ andheavy hydrocarbons.

According to one embodiment, the apparatus 100 comprises a reductionreactor 10, the carbon dioxide removal unit 38 and the heater 42. Theapparatus 100 comprises the reducing gas circuit 20 which passes throughthe carbon dioxide removal unit 38 and the heater 42 and the reactor 10.According to one embodiment, the apparatus 100 comprises first injectionmeans 49 a configured to feed, into the reducing gas circuit 20 betweenthe reducing gas heater 42 and the reduction reactor 10, the stream F2of fresh reducing gas which amounts to more than 20% of the quantity ofreducing gas needed to operate the direct reduction process.

In possible implementations, the first injection means 49 a areconfigured to feed the stream F2 of fresh reducing gas which amounts tomore than 25%, or 30%, or 35%, or 40%, or 45%, or 50%, or 55%, or 60%,or 65%, or 70%, or 75%, or 80%, or 85%, or 90%, or 95%, of the amount ofreducing gas needed to operate the direct reduction process.

In some embodiments, the apparatus 100, as indicated above, can includea control unit 68 to control the first injection means 49 a for thestream F2, and possibly one and/or the other of other injection means 49b, 49 c provided for the streams F3, F4 as described in detail below.The control unit 68 regulates at least the flow rate of the freshreducing gas stream F3 so as to maintain the sum of the heat provided bystream F2 plus the heat provided by stream F3 within a predeterminedrange of values so as to maintain the operating conditions of thereduction zone 12 of the reactor 10 to produce DRI at a predeterminedproduction rate. In some embodiments, the control unit 68 additionallyto regulating the flow rate of fresh reducing gas stream F2 alsoregulates the flow rate of fresh reducing gas stream F4.

In some embodiments, the first injection means 49 a are connected atexit from the heater 42. The heater 42 receives the stream F2 from anentry pipe 29 associated with a source 46 of reducing gas. A by-passbranch 60 a is advantageously associated with the pipe 29 and with thefirst injection means 49 a, in order to allow to by-pass at least thefeed of a part of the second stream F2 of fresh reducing gas to theheater 42 and inject it, instead, directly into the first injectionmeans 49 a.

In a possible embodiment, the apparatus 100 comprises, as mentionedabove, other one or more injection means 49 b, 49 c configured to injectinto the reducing gas circuit 20 at least the stream F3, F4 of freshreducing gas which amounts to the portion of reducing gas not injectedinto the reducing gas circuit 20 by the second stream F2.

In a possible embodiment, injection means 49 b are provided configuredto inject the stream F3 in correspondence with any portion whatsoever ofthe reducing gas circuit 20 located between the carbon dioxide removalunit 38 and the reducing gas heater 42. According to some embodiments, asource 44 of reducing gas, associated with the injection means 49 b, canbe provided to supply the stream F3 of fresh reducing gas.

In another possible embodiment, injection means 49 c are providedconfigured to feed the stream F4 directly into the reactor 10. Accordingto some embodiments, a source 48 of reducing gas, associated with theinjection means 49 c, can be provided to supply the stream F4 of freshreducing gas.

In further embodiments, it can be provided that both the injection means49 b and also the injection means 49 c are present, in order to feed acombination of reducing gas which amounts to the portion of reducing gasnot injected by the stream F2, formed by the stream F3 injected incorrespondence with any portion whatsoever of the reducing gas circuit20 located between the carbon dioxide removal unit 38 and the reducinggas heater 42, and by the stream F4 injected directly into the reactor10.

In one embodiment, the reduction reactor 10 is of the gravitationaltype.

In one embodiment, the reduction reactor 10 comprises a reduction zone12, inside which the iron ore reduction processes occur, feeding means16 to feed iron ore 15 into the reactor 10, an aperture 13 to extractspent reducing gas and a discharge zone 14 to discharge reduced iron 18.

In one embodiment, the reducing gas circuit 20 is configured toregenerate the spent reducing gas exiting the reactor 10 and re-injectit into the reactor 10 once it has been regenerated.

In one embodiment, the apparatus 100 comprises:

devices 32, 34, 36, 40 for regenerating the spent reducing gas,

the source 44 of reducing gas connected to the reducing gas circuit 20before the heater 42,

a suitable source 52 of oxygen connected to the reducing gas circuit 20between the heater 42 and the reactor 10,

the source 46 of reducing gas connected between the heater 42 and thesource 52 of oxygen,

the source 48 of reducing gas connected directly to the reactor 10;

a valve 56 disposed on the injection means 49 b, a valve 58 disposed onthe entry pipe 29, a valve 60 disposed on the by-pass branch 60 a, and avalve 62 disposed on the injection means 49 c;

the at least one control unit 68, which can be connected to at least oneof the valves 56, 58, 60, 62 and configured to regulate the respectivestreams F2, F3, F4 in response to signals emitted by the flowratesensors 69, 70.

In other embodiments (not shown), the at least one control unit 68 maybe connected to the source 52 of oxygen and configured to regulate itsflowrate.

According to some embodiments, the stream F1 of spent reducing gasexiting the reactor 10 can be injected into the reducing gas circuit 20by means of an aperture 13 connected to the reducing gas circuit 20.

In particular, the stream F1 of spent reducing gas reaches, by means ofa pipe 21, a heat exchanger 32 suitable to reduce the temperature of thegas.

The cooled reducing gas can be sent to a cooling tower 34 by means of apipe 22. In the cooling tower 34, the gas is further cooled and issubstantially deprived of the water component.

The water extracted from the gas by the cooling tower 34 can be conveyedin a pipe 25, by means of pumping means 66, in order to be reused insubsequent gas treatments described below, in particular to betransferred to a humidifier 40 described below.

Possible inert gases present in the spent reducing gas, and thereforenot useful for the reduction processes, can be extracted from thereducing gas circuit 20 through a pipe 23 on which a vent valve 54 isdisposed, to control the pressure of the circuit.

According to some embodiments, the inert gases exiting the vent valve 54can possibly be reinjected into the reducing gas circuit 20 toparticipate in other functions as described below.

The reducing gas which remains inside the reducing gas circuit 20, whichis not extracted through the vent valve 54, is directly fed through apipe 24 connected to the pipe 23, to a pumping means 64.

The gas exiting from the pumping means through the pipe 24 is sent to acooler 36, configured to decrease the temperature of the gas.

In some embodiments, the reducing gas circuit 20 of the reductionapparatus 100 described here comprises at least the carbon dioxideremoval unit 38 configured to remove CO₂ from the reducing gas.

According to some embodiments, the carbon dioxide removal unit 38 islocated downstream of the cooler 36 and connected to it by means of apipe 26.

According to some embodiments, the carbon dioxide removal unit 38 can beof the chemical absorption type where the CO₂ is absorbed by a solvent,for example, amines or potassium carbonate.

According to other embodiments, the carbon dioxide removal unit 38 canbe of the physical adsorption type where the CO₂ is adsorbed by a solidsubstrate.

In preferred embodiments, the carbon dioxide removal unit 38 can bedisposed at a point of the reducing gas circuit 20 so that it receivesthe reducing gas which has been treated by the treatment devices 32, 34,36.

In accordance with further embodiments, the carbon dioxide removal unit38 can be disposed before the spent reducing gas is mixed with freshreducing gas.

The reducing gas purified of the CO₂, or process gas, exits from thedevice 38 through a pipe 27 to reach the humidifier 40.

Some embodiments provide that in correspondence with the pipe 27, thesource 44 of reducing gas suitable to inject the stream F3 of freshreducing gas into the circuit can be connected through the injectionmeans 49 b.

The possible injection of fresh reducing gas of the stream F3 and itsvolume can be controlled by the valve 56 which controls the flowratetoward the pipe 27.

The process gas exiting from the carbon dioxide removal unit 38,possibly mixed with reducing gas coming from the stream F3, can reachthe humidifier 40 in which the percentage of water in the gas can beincreased up to a desired value by means of the direct contact of thegas with hot water.

According to some embodiments, the humidifier 40 can use, for itsfunction, the water extracted by the cooling tower 34, which isconnected to the humidifier 40 by means of a pipe 25 provided with thepumping means 66.

The humidified gas reaches, by means of a pipe 28, the heater 42 inwhich it is heated, for example up to a temperature comprised between800° C. and 1000° C.

The heater 42 functions by burning a suitable fuel introduced into theheater 42 by a supply source 50.

According to some embodiments, the suitable fuel can be fresh reducinggas, reducing gas extracted by the vent valve 54 or a combinationthereof.

According to some embodiments, the vent valve 54 can then be connectedto the fuel supply source 50.

Some embodiments provide that the source 46 of fresh reducing gas isconnected to a convective zone 43 of the heater 42 through the entrypipe 29. According to some embodiments, the pipe 29 can divide followinga path external to the convective zone of the heater 42 by means of theby-pass branch 60 a.

In accordance with some embodiments, the source 46 of fresh reducing gasor heavy hydrocarbon gases is connected to the reducing gas circuit 20between the heater 42 and the reactor 10 by the injection means 49 a.

Some embodiments can provide that the valve 58 and/or the valve 60 areable to direct and control the second stream F2 toward the heater 42, inparticular the respective convective zone 43.

In particular, the valve 58 is used to control the overall stream F2,while the valve 60, disposed on the by-pass branch 60 a, is used to varythe quantity of reducing gas that is injected into the heater 42.

Advantageously, the pre-heating allows to inject into the reducing gascircuit 20 reducing gas that is sufficiently hot for the subsequentsteps, so as to minimize the temperature drop resulting from the mixingof the fresh reducing gas with the reducing gas coming from the heater42.

According to some embodiments, between the injection means 49 a and thereactor 10, the source 52 of oxygen can be provided, configured toinject oxygen so as to increase the temperature of the incoming gas upto a temperature level comprised between 950° C. and 1150° C. Thisinjection of oxygen also allows to compensate for the temperature losscaused by mixing the fresh reducing gas, cold or pre-heated, with thereducing gas coming from the heater 42.

The regenerated gas can then be injected into the reactor 10.

It is clear that modifications and/or additions of parts or steps may bemade to the apparatus for the direct reduction and its correspondingmethod as described heretofore, without departing from the field andscope of the present invention.

It is also clear that, although the present invention has been describedwith reference to some specific examples, a person of skill in the artshall certainly be able to achieve many other equivalent forms of plantsfor direct reduction, having the characteristics as set forth in theclaims and hence all coming within the field of protection definedthereby.

In the following claims, the sole purpose of the references in bracketsis to facilitate reading: they must not be considered as restrictivefactors with regard to the field of protection claimed in the specificclaims.

1. A method for producing DRI in a direct reduction process using a reducing gas chosen among a natural gas having a high content of total hydrocarbons heavier than methane, or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH₄ and heavy hydrocarbons, said method comprising circulating a first stream (F1) of reducing gas exiting a reactor (10) in a reducing gas circuit (20) through at least one carbon dioxide removal unit (38), a reducing gas heater (42) and said reactor (10); and feeding, into said reducing gas circuit (20), between said reducing gas heater (42) and said reduction reactor (10), a stream (F2) of fresh reducing gas which amounts to more than 20% of the overall quantity of fresh reducing gas sent to the reduction reactor (10).
 2. The method as in claim 1, wherein said gas stream (F2) is pre-heated to a temperature lower than 650° C.
 3. The method as in claim 2, wherein said stream (F2) is pre-heated in a convective zone (43) of said reducing gas heater (42).
 4. The method as in claim 2, wherein said stream (F2) is pre-heated in a heat exchanger or fired heater separated from said reducing gas heater (42).
 5. The method as in claim 1, wherein said stream (F2) is injected into the circuit (20) without being pre-heated.
 6. The method as in claim 1, the method further comprising feeding at least one further fresh stream (F3, F4) of said fresh reducing gas which amounts to the portion of fresh reducing gas not injected into the reducing gas circuit (20) by the stream (F2).
 7. The method as in claim 6, wherein said stream (F3) is injected in correspondence with any portion whatsoever of the reducing gas circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42).
 8. The method as in claim 6, wherein it feeds said stream (F4) directly into the reactor (10).
 9. The method as in claim 6, the method comprising feeding a combination of said fresh reducing gas which amounts to the portion of fresh reducing gas not injected by the stream (F2), formed by the stream (F3) injected in correspondence with any portion whatsoever of the circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42), and by the stream (F4) injected directly into the reactor (10).
 10. The method as in claim 1, wherein at least the stream (F2) is controlled by at least one control unit (68) configured to regulate flow rate and therefore the percentage of said fresh reducing gas injected into the circuit (20).
 11. The method according to claim 10, wherein said control unit (68) regulates the flow rate of said gas stream (F2) in response to a signal emitted by a flow rate sensor (69, 70) measuring the flow rate of gas stream (F3) and/or (F4).
 12. The method as in claim 10, wherein said control unit (68) additionally to regulating the flow rate of said gas stream (F2) also regulates the flow rate of gas stream (F3) and/or (F4).
 13. The method as in claim 10, wherein said control unit (68) regulates at least the flow rate of the stream (F3) so as to maintain the sum of the heat provided by stream (F2) plus the heat provided by stream (F3) within a predetermined range of values so as to maintain the operating conditions of the reduction zone (12) of the reactor (10) to produce DRI at a predetermined production rate.
 14. The method as in claim 10, wherein said control unit (68) also regulates a flow rate of oxygen (52) with the aim of compensating the loss of energy caused by the fact that gas stream (F2) bypassing the fired heater (42) will not have in any case the same temperature of the pipe (28) after heating in same fired heater (42).
 15. The method as in claim 1, wherein said method does not comprise any step of removal of the fraction of heavier hydrocarbons from the reducing gas, in particular it does not comprise any reforming step.
 16. An apparatus for producing DRI from direct reduction of iron ore using a reducing gas having a high content of hydrocarbons heavier than methane, chosen among a natural gas having a high content of hydrocarbons heavier than methane, or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH₄ and heavy hydrocarbons, said apparatus comprising a reduction reactor (10), a carbon dioxide removal unit (38) and a heater (42), a reducing gas circuit (20) being provided which passes through said carbon dioxide removal unit (38) and said heater (42) and said reactor (10), said apparatus comprising a first injection means (49 a) configured to feed, into said reducing gas circuit (20) between said reducing gas heater (42) and said reduction reactor (10), a stream (F2) of fresh reducing gas which amounts to more than 20% of the quantity of reducing sent to the reduction reactor (10).
 17. The apparatus as in claim 16, wherein the apparatus comprises further injection means (49 b, 49 c) configured to inject into the reducing gas circuit (20) at least one fresh stream (F3, F4) of said reducing gas which amounts to the portion of reducing gas not injected into the reducing gas circuit (20) by the stream (F2).
 18. The apparatus as in claim 17, wherein said injection means (49 b) are configured to inject said stream (F3) in correspondence with any portion whatsoever of the reducing gas circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42).
 19. The apparatus as in claim 17, wherein said injection means (49 c) are configured to feed said stream (F4) directly into the reactor (10).
 20. The apparatus as in claim 16, wherein the apparatus comprises at least one control unit (68) connected to at least one of valves (56, 58, 60, 62) and configured to regulate the respective streams (F2, F3, F4).
 21. The apparatus as in claim 20, wherein the at least one control unit (68) is connected to the source (52) of oxygen and configured to regulate its flowrate.
 22. The apparatus as in claim 16, wherein said apparatus does not comprise any means or device for removal of the fraction of heavier hydrocarbons from the reducing gas, in particular it does not include any reformer. 